What causes fewer women than men to choose high-earning potential subjects such as engineering, economics or science at undergraduate level? This column presents new evidence from an accidental natural experiment in Italy, suggesting mixed-gender classes at the high-school level reduce the number of women pursuing these subjects. These results suggest that gender-separated classrooms are an effective way to increase women’s career opportunities and salaries.

Gender gap in college majors and earnings

In most European and North American countries women have overtaken men in college graduation rates. Nevertheless, a striking gender gap persists in the salaries of men and women, even when they are highly educated – and even if the overall gap has, in fact, narrowed in some nations (Black and Spitz-Oener 2007). One important reason for that gap is that men and women choose different college majors leading to very different careers. Nearly two thirds of all humanities degrees are awarded to women. Men, instead, choose majors in engineering, economics and in the mathematical sciences in much larger proportions. In the US, about 80% of recent graduates in engineering were male. In turn, the choice of college major correlates strongly with earnings and career opportunities. For example, in 2011, US students of engineering had an average yearly salary of almost $55,000 after graduation. Newly minted graduates from humanities majors instead earned only about $31,500.

New evidence

In a recent study (Anelli and Peri 2013) we ask if the gender composition of the high-school class attended by an individual affects his/her choice of study programme and subsequent long-term earning potentials. We use data that we collected on 30,000 students in Italian high schools over the period 1985-2005, including information on their high school, college career, family background and income as of 2005. We find that the gender ratio of high-school classmates significantly affected their choice of college major. In particular, women who attended a high-school class with a significant larger percentage of other female students (more than 75%) were significantly more likely to go on to choose college majors leading to high-paying jobs, namely engineering, economics, business and medicine. Those are also majors typically dominated by male students. On the other hand, female students in classes with a balanced gender mix were more likely to choose typically ‘female’ majors, that is, largely in the humanities and arts, and leading to lower earnings and limited overall career potential.

The effect of mixed-gender high-school classes

Our study details that – controlling for academic quality, high school and family background – these high-school students from Milan, Italy, were accidentally and randomly assigned to classes with a larger or smaller share of boys and girls. This accidental feature had a significant and long-lasting effect on the students: evidence suggests that a larger share of students of the same gender in the class increased the probability of choosing a high-earning college major. This finding is true for both men and women. In particular, as shown in below, women in high-school classes with more than 75% women had a 5-6% higher probability to choose high-earning majors than women in classes with a high percentage of men. Similarly, men in classes of more than 75% of women had a 6-7% higher probability of choosing high-earning majors.

Interestingly, these effects seem last longer for women. Those who attended classes with a large percentage of women and then choose high-earning majors also graduated from them and performed better than or as well as other women in those majors. Hence the long-run effect for women was a higher probability of graduating from high earning majors and therefore higher expected wage. On the other hand men who attended classes with high percentage of men had a higher probability of enrolling in high-earning majors but were also more likely to drop out. Thus, they did not have a higher probability of graduating from these potentially high-earning majors. Moreover women from classes with a large female percentage had higher wages on the labour market relative to other women above and beyond, that is, controlling for, the effect driven by their programme of study.

Overall, the expected wage premium for a woman who attended a high-school class with female share above 75% relative to an identical one who attended a class with a female share below 25% was €1,110 (about $1,470). This wage premium represents an expected 5.3% wage increase, as large as the return of one extra year of schooling in Italy!

Explaining the effect

The high school years (13 to 18 in Italy) are crucial for young women in shaping their preferences and self-confidence. In part, girls may shape those attributes by comparing themselves to male students. If there are fewer men for comparison, they may more readily consider themselves to be good at math, or interested in science, or fascinated by technology, attributes our society stereotypically assigns to men. Recent experimental research shows that gender-specific roles may be perpetuated at the high-school level (see Mobius et al. 2012 on how women and men adjust their beliefs about themselves). With fewer men around, some women are freer to choose to pursue what they love and what they are good at.

Policy implications: gender separation in high-school classes

Interestingly, the policy implications of these findings are straightforward. If an objective of schooling is to increase women’s career opportunities and thereby their salaries, our results would suggest that gender-separated classrooms would be an effective step in the right direction. Incidentally, men will also benefit, being encouraged to enroll in high-earning majors. Gender-separated classrooms would increase the probability of choosing high-earning majors for both women and men. At the very least, schools could offer students the possibility of choosing single-sex classes. Or they could offer students the possibility of entering a random lottery to be in single-sex classes and, through observing their subsequent college choice, we would be able to continue to test the effect of peer gender.

Figure 1. Probability of enrolling in a high-earning major as a function of classroom same-sex ratio